Lubricating oils for heavy duty diesel engines require crankcase lubricating oils which stabilize against oxidation and which limit the formation of engine deposits. In addition, these crankcase lubricating oils must also have a high alkalinity reserve to neutralize acids formed during fuel combustion.
Many heavy duty locomotive and marine diesel engines in use in the United States and other countries pose an additional lubrication problem. Typically, the older heavy duty diesel engines have silver-surfaced engine parts, such as silver or silver-plated bearings. The silver-plated bearings provide improved fatigue strength and load carrying capacity, along with superior lubricity and corrosion resistance over the older needle bearings. Unfortunately, these silver-plated bearings are incompatible with many conventional additives in lubricating oils for heavy duty diesel engines. Furthermore, silver or silver-plated bearings pose a special problem since many of the bearing protective additives, such as zinc di-alkyl di-thiophosphates, which are effective to protect bearings surfaced with other materials, for example, brass, copper, lead, bronze and aluminum, are corrosive to silver or silver-plated bearings.
In the past, silver protection was largely provided by the use of lubricating oils containing chlorinated paraffins, long chain fatty acids and sulfur-containing compounds. However, chlorinated compounds are perceived as having environmental problems and high sulfur-containing compounds have other undesirable effects. Therefore, there is a great need for lubricating oils which do not have the drawbacks discussed above, but provide silver protection. A number of patents have disclosed lubricating oil compositions for silver protection, but none have provided the enhanced protection observed with the lubricating oil composition of the present invention.
Great Britain Patent No. 1,415 964 discloses a composition of additives conferring anti-wear properties to the lubricant with which it is incorporated, without making that lubricant corrosive to silver. The composition contains (A) a triester of phosphorothionic acid, and (B) a triester of ortho-phosphoric acid, or (C) a mixture of hydrocarbyl phosphates of organic bases.
Canadian Patent No. 810120 discloses a lubricating oil composition comprising the reaction product obtained by the neutralization with an alkaline earth metal oxide or hydroxide of a sulfurized alkyl phenate in admixture with a Mannich base reacted with carbon dioxide. The patent suggests that the lubricating oil of the invention is likely to protect silver bearings in railway diesel engines.
U.S. Pat. No. 2,959,546 discloses the use of formaldehyde and/or any compound which will readily decompose to give free formaldehyde to effectively inhibit silver corrosion caused by sulfurized and phosphor-sulfurized additives without interfering with the oxidation inhibiting or other desirable properties of these sulfur-containing additives.
U.S. Pat. No. 3,267,033 discloses a novel composition of matter comprising from about 1 to 3 parts by weight of an oil-soluble fatty acid having at least 12 aliphatic carbon atoms in the fatty radical and from about 1 to 3 parts by weight of a tertiary-aliphatic primary amine salt of a partially esterified phosphoric acid in which the ester radical has from 1 to about 30 aliphatic carbon atoms. The composition imparts desirable frictional characteristics to lubricants.
U.S. Pat. No. 3,649,373 discloses a silver passivating composition consisting of a carrier inert to silver and a thiocarbamic compound.
U.S. Pat. No. 3,775,321 discloses lubricating oil compositions comprising alkali and alkaline earth metal phenates, chlorinated hydrocarbonaceous components, sulfur-containing compounds, naphthyl amines and diamine components which exhibit improved resistance to wear in both silver and bronze engine components.
U.S. Pat. No. 4,169,799 discloses a lubricating oil composition containing a combination of components consisting of an overbased alkaline earth metal containing alkylphenolate and a chlorinated sulfurized alkylphenol.
U.S. Pat. No. 4,244,827 discloses mixtures of di- or tri-thiophosphoric acids di-esters produced from 1,2-diols or 1-mercapto-2-hydroxy compounds by reaction with P2S5 as excellent stabilizing agents for lubricants.
U.S. Pat. No. 4,278,553 discloses a railway diesel lubricating oil containing a silver corrosion inhibitor comprising a benzotriazole compound present in concentrations from about 0.5 to 2.0 weight percent.
U.S. Pat. No. 4,285,823 discloses a silver corrosion inhibitor for railway diesel engine lubricating oils comprising an N-alkylaminomethyl-5-amino-1H-tetrazole.
U.S. Pat. No. 4,575,431 discloses a lubricating oil additive comprising a mixture of phosphates, said phosphates being essentially free of mono-thiophosphates and comprising (a) di-hydrocarbyl hydrogen di-thiophosphates; and (b) a sulfur-free mixture of hydrocarbyl di-hydrogen phosphates, said composition being at least 50% neutralized by a hydrocarbyl amine having 10 to 30 carbons in said hydrocarbyl group.
U.S. Pat. No. 4,717,490 discloses a lubricating oil containing (1) an alkali metal borate; (2) an oil-soluble sulfur compound; (3) a di-alkyl hydrogen phosphate; and (4) a mixture of neutralized phosphates said phosphates being essentially free of mono-thiophosphates which interact synergistically to provide a lubricant with superior load carrying properties.
U.S. Pat. No. 4,764,296 discloses a lubricating oil composition for railway diesel engines which comprises a lubricating oil base, an ashless dispersant, a mixture of an overbased alkaline earth metal alkylphenolate and alkyl sulfonate compounds and a polyhydroxy compound of up to 60 carbon atoms or a mixture of a polyhydroxy compound of up to 60 carbon atoms and a chlorinated hydrocarbon.
U.S. Pat. No. 4,820,431 discloses a lubricating oil for protection against silver wear in railway diesel engines which is formulated with no chlorinated hydrocarbons or with reduced levels thereof. The composition comprises a silver protective compound selected from the group consisting of (1) C8 to C22 fatty acid esters of C1 to C12 polyhydroxy alcohols or mixtures of such esters and (2) a mixture comprising the polyhydroxy compound of (1) above, and a chlorinated paraffin.
U.S. Pat. No. 5,244,591 discloses essentially chlorine-free lubricating compositions having a TBN of 10-30 designed for use in internal combustion engines having silver bearing parts which provide protection for said bearings via incorporation therein of certain unsaturated aliphatic carboxylic acids.
U.S. Pat. No. 5,302,304 discloses a method of protecting silver parts and inhibiting copper corrosion in an internal combustion engine and a silver-wear and copper-wear protection additive in a lubricating composition comprising a major proportion of an oil of lubricating viscosity and a minor amount of a silver-wear and copper-corrosion protection additive comprising the reaction product of an amine, formic acid and a C5 to C60 carboxylic acid.
U.S. patent application Ser. No. 10/463,932 (Publication No. US 2004/0259743 A1) discloses a lubricating oil composition containing: (1) an anti-wear package comprising: (a) a hydrocarbyl phosphate and amine salt thereof; and (b) an alkylene coupled adduct of a hydrocarbyl substituted dithiophosphoric acid and an α,β-unsaturated carbonyl containing compound; (2) an anti-oxidant package comprising: (a) a hydrocarbyldiphenylamine; and (b) a sterically hindered phenol; (3) a metal deactivator; and (4) an oil of lubricating viscosity. The invention further relates to the process to make the lubricating oil composition and its use in industrial fluids, especially hydraulic fluids.
U.S. patent application Ser. No. 10/630,026 (Publication No. US 2005/0026791 A1) provides an oil-soluble lubricant additive package comprising at least one hydrocarbylamine salt of a di-alkyl mono-thiophosphate. The object of the invention therein is to provide an additive package which can be used to formulate a low sulfur, low ash and low phosphorus content oil for use in gasoline or diesel engines.